This invention relates to stable polyol mixtures ontaining mixtures of internal mold release agents and optionally other auxiliaries.
Rigid, semi-rigid and flexible polyurethane materials are often produced by machine-mixing a polyol mixture with a polyisocyanate and introducing the resulting mixture into a mold in which the reaction mixture subsequently cures, optionally with formation of layers differing in density. The mold may be made of any of a variety of materials (for example steel, aluminum or epoxy resin) and may be heated or unheated.
The demoldability of the workpiece formed from the reaction mixture is improved by using so-called external release agents or release lacquers or internal release agents. Tile external release agents are injected into the mold. The so-called internal release agents are incorporated in the reaction mixture and lead to good demoldability of the workpiece (molding) formed with no need for external release agents. Internal release agents may be added to the isocyanate component of the reaction mixture or preferably to the polyol component of the reaction mixture or to both components before these components are combined in the mixing machine.
internal release agents are often products containing aliphatic paraffin chains which, in general, should contain more than 10 carbon atoms. Reaction products or derivatives of long-chain fatty acids, more particularly natural fatty acids, such as oleic acid, tall oil fatty acid, stearic acid, palm kernel oil fatty acids, train oil fatty acids, ricinoleic acids, linoleic acids, erucic acids or mixtures thereof, are preferably used.
Derivatives or reaction products of such fatty acids which may be used as mold release agents include the hydrogenation and reduction products of those acids, esterification or amidation products of those acids, salts, urethanes or esters of such esterification or amidation products, amine salts of such fatty acids or addition products (for example, with carbodiimides) or the products obtained in Passerini or Ugi multi-center reactions.
Among the internal release agents, two types have proven to be particularly effective over the years. The first of these types contains an NH function either through amine bonds or through urethane bonds in the molecule. The second type contains amine salt functions which themselves may also contain amide functions. Both basic types may also have ester groups.
Examples of salt-like release agents include the oleic acid salt of the amide of 1 mol N-dimethyl-1,3-propylenediamine and oleic acid and the ester of 1 mol N-dimethyl ethanolamine and oleic acid. Examples of non-salt-like types of internal release agents containing -NH functions include the reaction product of diisocyanatodiphenyl methane types (i.e. polyisocyanates) with the ester of, for example, 1 mol pentaerythritol and 2 to 3 mol oleic acid or even the oleic acid amide of 1 mol oleic acid and the oleic acid ester of ethanolamine.
Both the non-salt-like release agents containing urethane or ester groups and the release agents containing salt groups are particularly suitable for use as internal release agents.
The polyol mixtures used for the production of moldings from polyol and polyisocyanate mixtures as described above frequently contain short-chain polyols (i.e., polyols produced from polyalcohols and/or (poly)amines by alkoxylation to OH values above 700), polyols of medium chain length (i.e., products reacted in the same way, but by more productive alkoxylation to OH values between 100 and 700), and long-chain polyols (i.e., products reacted in basically the same way, but to OH values of 8 to 100).
It is, of course, also possible to use short-chain, medium-chain or long-chain polyols characterized by the OH value ranges mentioned which have been produced by any method. Polyesters, polyamides, polyurethanes, polyols which have not been subjected to further modification (for example, glycerol, sugar products, formoses, etc.), the so-called polymer polyols, filler-containing polyols, so-called PHD polyols and other polyols and polyol mixtures containing polyisocyanate reaction products in the form of a stable dispersion may be used to produce molded materials.
In addition, polyol mixtures to be used in the production of molded articles often contain special pore stabilizers. optionally oxidation or radiation stabilizers, colorants, fragrances or other active substances, small quantities of water and optionally additional blowing agents.
DE-OS 1,953,637 describes a process for the production of foams by foaming a reaction mixture of polyisocyanates, compounds containing reactive hydrogen atoms, water and/or organic blowing agents and also additives in a closed mold. The salts of aliphatic carboxylic acids and primary amines or amide- and/or ester-modified amines containing at least 25 aliphatic carbon atoms may be used as additives.
DE-OS 2,307,589 describes a process for the production of foams based on polyisocyanates, in which the foams are produced in closed molds using reaction products of fatty acid esters and polyisocyanates and optionally other release agents. Oleic acid and tall oil fatty acid salts of the amide-modified amine (obtainable by reaction of N-dimethylaminopropyl amine with oleic acid or tallow oil fatty acid) are disclosed as optional release agents.
In the process disclosed in DE-OS 2,121,670, the foam moldings are produced using mixtures of at least two of the following components:
a) salts of aliphatic carboxylic acids and optionally amide-and/or ester-modified amines, PA1 b) COOH- and/or OH-functional esters of monobasic and/or polybasic carboxylic acids, PA1 c) natural and/or synthetic oils, fats or waxes.
and
It has now been found that, in particular, the highly effective internal release agents of the type described above (for example the release agents containing urethane NH groups), tend to form unstable mixtures and to "float off" when added to the polyol mixtures in the relatively large quantities required for good demolding.
It is also known that mixtures of several release agents can be used as an internal release agent in the production of moldings, optionally even in the polyol and polyisocyanate phase, if it is desired to obtain particularly good release effects.
However, all of the known systems have the disadvantage that it is not possible to produce stable preparations (i.e., preparations storable for the prolonged periods typically involved in the transport and storage of polyurethane raw materials), with them. The polyol mixtures typically used in the production of moldings and the internal release agents are often largely incompatible, particularly when the release agents are added in quantities of more than 5%.